Summary:
Prior to this PR it prints the raw bytes which can include non-printable
characters. This PR adds the option to print in hex instead.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/7820
Test Plan:
try it out
```
$ ./ldb file_checksum_dump --hex --db=/tmp/rocksdbtest-9383//db_basic_test_12281129388755189514/
16, FileChecksumCrc32c, 0xC789D948
```
Reviewed By: jay-zhuang
Differential Revision: D25738072
Pulled By: ajkr
fbshipit-source-id: 8cf2856877971756c0495cfa63a9a1281c414dc7
b8c01ed38a